This disclosed embodiment relates to a touch-screen display system for generating pixel coordinate estimates responsive to a user touching (pressing a key on) a display screen, and more particularly relates to improving the efficiency of generating such pixel coordinate estimates through enhanced techniques of calibration and validation of the estimates.
In a typical touch-screen display system, an x-axis coordinate position is sampled and then a y-axis coordinate position is sampled to indicate a pixel location where a user has touched the display screen. If the samples are corrupted by noise or by drift of some parameter of the system, then these samples yield an incorrect indication of where the user has touched the display screen.
Typically, the system is controlled to insert timing delays into the sampling process to allow the various x-axis and y-axis drivers to settle out as they are switched back and forth between x and y so noisy estimates are avoided.
Calibration routines are typically run which require the user to assist in this calibration effort by touching various known locations on the display screen and/or require implementing look-up tables and pre-calibrated cables in the system.
Also, in many touch-screen display systems, only an active touch of the display screen (or apparent touch caused by system noise) is detected. Detecting the absence of a touch (key press) and reducing the possibility of a false touch caused by noise is often just as desirable as detecting the position of an active touch.
U.S. Pat. No. 6,246,394 to Kalthoff et al. includes a conventional analog resistive touch-screen display assembly 2. It employs a 4-wire arrangement for taking measurements. U.S. Pat. No. 6,016,140 to Blouin et al. is directed to a system and method that uses look-up tables and calibration cables for calibration. U.S. Pat. No. 5,751,276 to Shih is directed to a method for calibrating touch panel displays using mapping transfer information. U.S. Pat. No. 5,241,139 to Gungl et al. determines the position of a member contacting a touch screen by tracking coordinates. U.S. Pat. No. 4,145,748 to Eichelberger et al. includes a charge transfer analog-to-digital converter for a digital reading obtained for a “no touch” condition stored in memory, comparing digital readings from each pad to the “no touch” reading stored in memory.
An approach to generating pixel coordinate estimates that minimizes sampling delays, reduces corruption of estimates due to noise, eliminates the need for user-interactive calibration, enhances ESD protection, or provides more than one of these features is desired.